The paper by Ross and al. is based on contrasting features of the tale AT 480 as presented by Roberts (1958). In their use of these data, the authors carried out problematic, non-explicit operations, and they made factual errors when counting the occurrences. These problems are indicative of a lack of rigor and call into question the relevance of their work.

I – Logical dependencies between the features.

One matter of concern in this paper is the logical dependencies between the features (see Supplementary Table S2). The authors are obviously aware that a number of these features are hierarchically structured, ant they illustrate the structure by levels of indent in the table. For instance:

VI B1 Helper advises heroine

VI B1a Helper advises heroine to demand objects one at a time

VI B1b Helper advises which reward to choose

VI B1c Helper advises heroine to demand objects one at a time

VI B1d Door (variable created by Ross and all)

VI B1d1 Not to open the door

VI B1d2 Helper advise heroine to open door

The problem is that a "yes" on item B1d1 or B1d2 implies a "yes" on items B1d and B1. This can affect the results of the analysis by exaggerating the clustering. Some clusters are created artificially by the logical structure of the questionnaire rather than by the historical processes the authors are trying to detect.

1. There are 11 (and not 10) versions that check the feature D1 as indicated in the column D1(Eu).

2. The disparition of the feature D5 ("other") in the authors’s tables (cf. Supplementary Table S1) can be explained by their explicit choice to exclude the traits coded as "other" ("traits coded as ‘other’ were excluded because it is a catchall category"); yet that does not justify the suppression of the trait D3 "goats" that is found in a Latvian version. In this table, one can see that none of the traits selected by Ross and al. are <2 ; this suggest that the unique trait were systematically eliminated.

1. There are 14 occurrences of trait II A2a, not 13 as indicated by Ross et al.

2. As seen above, the authors explain that they exclude the traits coded as "other" ("traits coded as ‘other’ were excluded because it is a catchall category such that a shared presence of ‘other’ does not represent similarity"); yet it can be seen that the trait 2d "other" was included in the total calculation of the versions that verifies the proposal A2 ("The main actors are sent for water") whose value 40 corresponds to the sum A2a-d (13+16+2+9). This operation could be justified, because "other" refers here to a place where there is water that is not "spring", "well" and "river"; however, this is in direct contradiction to the premise: "traits coded as 'other' were excluded".

3. The introduction of a numeric value for the generic trait II A2 is also problematic, compared to the treatment used for other traits. In the case of the previously seen VII D trait, the authors excluded VII D 5 "other". However, the generic trait VII D being "animal", VII D5 means "other animal", that is to say neither "herd of horse" (D1), nor "herd of cows" (D2), nor "goats" (D3), nor "sheeps" (D4). Therefore, the authors could have given a numeric value for VII D by summing D1-D5, as they did for II A2 by summing A2a-d. One cannot address the problem of the "groups of traits" by using different criteria in the same analysis ; this precludes any positive result.

IV – The origin of the problem

Ross et al. are an integral part of a long tradition in mythological studies, tradition which they do not seem to be aware of. Yet it is important to be conscious of the theorical origins of this work.

According to Carl Wilhelm von Sydow (who himself was following a long tradition, see Hafstein 2005), folktales are like biological beings. They tend to adapt to their environment and they evolve by means of natural selection. This explains why so many variants differ from general tale-types. As soon as 1909, Arnold van Gennep stated that folkloric elements should be studied ''comparatively, with the aid of the biological method'' (van Gennep 1909: 84). Starting in 1927, Von Sydow introduced the concept of oicotypification into folkloristics, that is to say "a certain unification of the variants within one and the same linguistic or cultural area on account of isolation from other areas" (von Sydow 1948: 238). He says that "changes brought about by various kinds of mutation, and by oicotypification, are naturally of the greatest weight for a scientific study of folklore" (von Sydow 1948: 239). In line with this approach, some recent works have then tried to apply phylogenetics to mythology (d'Huy 2012 a, b, c ; 2013 a, b), but Ross et al. do not mention their predecessors.

V – Folktale and popular litterature

According to the authors, most of the folktale variants they studied were collected during the late nineteenth and early twentieth centuries, before communication technology and air travel transformed the way ideas and people spread. Yet they forget the influence of popular litterature.

Versions of the "The tale of the kind and the unkind girls" have played a part in literary tradition: they are included in Basile's Pentamerone ("Le tre fate" ie "The Three Fairies", 1634), Peele's The Old Wives Tale and Shakespeare's The Merchant of Venice (for the motif of the choice among casket); Perrault's Contes de ma mère l'Oye ("Les fées" i.e. "The Fairies", 1697); Grimm's Children's and Household Tales ("Die drei Männlein im Walde", i.e. "The tree little men in the wood" and "Frau Holle", i.e. "Mother Holle", 1812), Bechstein's ("Goldmaria und Pechmaria", i.e. "Gold-Mary and Pich-Mary", 1845), Naubert's ("Der kurze Mantel", i.e. "The Cloak", 1789).

Yet during the 17th and the 18th centuries, a lot of chapbooks circulated first in European cities and then throughout rural areas around. These books borrowed their material from folk culture as well as from literary classics, and they touched whole social group, like farmers, artisans, and peasants.

For instance, in France, the easily available, crudely illustrated volumes that made up la bibliothèque bleue were often read during long winter evenings. Those who could not read listened to the readers and memorized the tales, while the contents were copied down by those who could write (Malarte-Feldman 2008: 120). After the first publication of Perrault's book, La Bibliothèque Bleue also republished his stories (Soriano 1958, Mandrou 1985). Yet the texts were often modified and simplified to make them more attractive and easier to read, though they were still published under Perrault’s name. Literary fairy tales finally returned to traditional folklore (Jean 2007: 281-282). Perrault’s and other popular authors’ influence on folklore is very important, as shown by the case of The Sleeping Beauty that has been folklorised, although the story was originally a literary tale (Jean 2007: 281-282). Into another linguistic area, the earlier oral versions of some Irish oral legends were eclipsed by a mid-eighteenth-century Irish chapbook by James Cosgrave, 2008: 181). Grimms' Fairy Tales were also very popular in their written form. On the other hand, some written version of the tale of The Kind and the Unkind Girls, as the Peele's one, remained little known and had no influence on the oral form of the tale (Roberts 1958: 121),

The flaw here is that litterary publications may allow a deeper structuration of a folktale in a specific linguistic area: each text was written in a certain language and it is most likely to spread where this language is spoken.

VI – The slow evolution of myths

Ross et al. suggest that language differences between cultures create stronger significant barriers to folktale diffusion than those for the exchange of genes. Folktale and language histories are decoupled, they say, because "the folktales spread much later than the spread of languages across Europe or because any legacy of deep cultural ancestry inherited down language lineages has been obscured by subsequent folktale evolution and geographical diffusion."

The reported data, however, could also suggest that folktale preserves themes and motifs that are more ancient than language. One of us (d'Huy 2013a) suggests that myths can show little evolutionary change for most of their history, evolving significantly only during rare and rapid events of branching speciation.

In agreement with this slow evolution, mythologies preserve themes and motifs that are very ancient. Claude Lévi-Strauss revealed that all the mythologies throughout the entire American continent ultimately derive from a single myth that the populations have gradually transformed through some mysterious impulse (1981: 563), and this is why a large part of the Amerindian mythology remained almost the same since the first settlement(s) ― albeit through many variants and inversions. For instance, the dance choreography of Brazilian Krahô-speakers today is similar to rock art images painted by their ancestors, 12000 years ago (Guidon and Buco 2006: 128). Creation myths of the northern part of the Meso-American area show a strong relationship with similar stories from the Pacific islands, and from East and South Asia; their distribution suggest an ancient channel of cultural contact between Eurasia and America (Hatt 1949a, Rooth 1957). The fact that many complex Eurasian and American myths are highly similar, as well as the congruence of many motifs in North America and North-East Asia, show that these stories could only spread when a former land bridge joined present-day Alaska and eastern Siberia during the Pleistocene ice ages (Berezkin 2004). These myths should be palaeolithic (Berezkin 2005a, b; Witzel 2013). Consequently, mythologies are stable and can conserve deeper signals than language.

The authors would like to thank Vincent Hirtzel for his help and his useful comments.